diff --git a/src/message.rs b/src/message.rs
index 81a7be82..68aca5de 100644
--- a/src/message.rs
+++ b/src/message.rs
@@ -161,23 +161,23 @@ impl<W: Write> WriteMessage for W {
                 try!(buf.write_cstr(portal));
                 try!(buf.write_cstr(statement));
 
-                try!(buf.write_u16::<BigEndian>(formats.len() as u16));
+                try!(buf.write_u16::<BigEndian>(try!(u16::from_usize(formats.len()))));
                 for &format in formats {
                     try!(buf.write_i16::<BigEndian>(format));
                 }
 
-                try!(buf.write_u16::<BigEndian>(values.len() as u16));
+                try!(buf.write_u16::<BigEndian>(try!(u16::from_usize(values.len()))));
                 for value in values {
                     match *value {
                         None => try!(buf.write_i32::<BigEndian>(-1)),
                         Some(ref value) => {
-                            try!(buf.write_i32::<BigEndian>(value.len() as i32));
+                            try!(buf.write_i32::<BigEndian>(try!(i32::from_usize(value.len()))));
                             try!(buf.write_all(&**value));
                         }
                     }
                 }
 
-                try!(buf.write_u16::<BigEndian>(result_formats.len() as u16));
+                try!(buf.write_u16::<BigEndian>(try!(u16::from_usize(result_formats.len()))));
                 for &format in result_formats {
                     try!(buf.write_i16::<BigEndian>(format));
                 }
@@ -215,7 +215,7 @@ impl<W: Write> WriteMessage for W {
                 ident = Some(b'P');
                 try!(buf.write_cstr(name));
                 try!(buf.write_cstr(query));
-                try!(buf.write_u16::<BigEndian>(param_types.len() as u16));
+                try!(buf.write_u16::<BigEndian>(try!(u16::from_usize(param_types.len()))));
                 for &ty in param_types {
                     try!(buf.write_u32::<BigEndian>(ty));
                 }
@@ -246,7 +246,7 @@ impl<W: Write> WriteMessage for W {
         }
 
         // add size of length value
-        try!(self.write_u32::<BigEndian>((buf.len() + mem::size_of::<u32>()) as u32));
+        try!(self.write_u32::<BigEndian>(try!(u32::from_usize(buf.len() + mem::size_of::<u32>()))));
         try!(self.write_all(&*buf));
 
         Ok(())
@@ -407,3 +407,25 @@ fn read_row_description<R: BufRead>(buf: &mut R) -> io::Result<BackendMessage> {
 
     Ok(RowDescription { descriptions: types })
 }
+
+trait FromUsize {
+    fn from_usize(x: usize) -> io::Result<Self>;
+}
+
+macro_rules! from_usize {
+    ($t:ty) => {
+        impl FromUsize for $t {
+            fn from_usize(x: usize) -> io::Result<$t> {
+                if x > <$t>::max_value() as usize {
+                    Err(io::Error::new(io::ErrorKind::InvalidInput, "value too large to transmit"))
+                } else {
+                    Ok(x as $t)
+                }
+            }
+        }
+    }
+}
+
+from_usize!(u16);
+from_usize!(i32);
+from_usize!(u32);
diff --git a/src/types/chrono.rs b/src/types/chrono.rs
index dc65b673..159bbdec 100644
--- a/src/types/chrono.rs
+++ b/src/types/chrono.rs
@@ -1,10 +1,12 @@
 extern crate chrono;
 
+use std::error;
 use std::io::prelude::*;
 use byteorder::{ReadBytesExt, WriteBytesExt, BigEndian};
 use self::chrono::{Duration, NaiveDate, NaiveTime, NaiveDateTime, DateTime, UTC};
 
 use Result;
+use error::Error;
 use types::{FromSql, ToSql, IsNull, Type, SessionInfo};
 
 fn base() -> NaiveDateTime {
@@ -61,8 +63,13 @@ impl FromSql for NaiveDate {
 
 impl ToSql for NaiveDate {
     fn to_sql<W: Write+?Sized>(&self, _: &Type, mut w: &mut W, _: &SessionInfo) -> Result<IsNull> {
-        let jd = *self - base().date();
-        try!(w.write_i32::<BigEndian>(jd.num_days() as i32));
+        let jd = (*self - base().date()).num_days();
+        if jd > i32::max_value() as i64 || jd < i32::min_value() as i64 {
+            let err: Box<error::Error+Sync+Send> = "value too large to transmit".into();
+            return Err(Error::Conversion(err));
+        }
+
+        try!(w.write_i32::<BigEndian>(jd as i32));
         Ok(IsNull::No)
     }
 
diff --git a/src/types/mod.rs b/src/types/mod.rs
index 5ad8eb56..49f5cc03 100644
--- a/src/types/mod.rs
+++ b/src/types/mod.rs
@@ -934,15 +934,15 @@ impl ToSql for HashMap<String, Option<String>> {
 
     fn to_sql<W: Write+?Sized>(&self, _: &Type, mut w: &mut W, _: &SessionInfo)
                                -> Result<IsNull> {
-        try!(w.write_i32::<BigEndian>(self.len() as i32));
+        try!(w.write_i32::<BigEndian>(try!(downcast(self.len()))));
 
         for (key, val) in self {
-            try!(w.write_i32::<BigEndian>(key.len() as i32));
+            try!(w.write_i32::<BigEndian>(try!(downcast(key.len()))));
             try!(w.write_all(key.as_bytes()));
 
             match *val {
                 Some(ref val) => {
-                    try!(w.write_i32::<BigEndian>(val.len() as i32));
+                    try!(w.write_i32::<BigEndian>(try!(downcast(val.len()))));
                     try!(w.write_all(val.as_bytes()));
                 }
                 None => try!(w.write_i32::<BigEndian>(-1))
@@ -959,3 +959,12 @@ impl ToSql for HashMap<String, Option<String>> {
         }
     }
 }
+
+fn downcast(len: usize) -> Result<i32> {
+    if len > i32::max_value() as usize {
+        let err: Box<error::Error+Sync+Send> = "value too large to transmit".into();
+        Err(Error::Conversion(err))
+    } else {
+        Ok(len as i32)
+    }
+}
diff --git a/src/types/slice.rs b/src/types/slice.rs
index cb9156b8..02cb3975 100644
--- a/src/types/slice.rs
+++ b/src/types/slice.rs
@@ -3,7 +3,7 @@ use byteorder::{WriteBytesExt, BigEndian};
 
 use Result;
 use error::Error;
-use types::{Type, ToSql, Kind, IsNull, SessionInfo};
+use types::{Type, ToSql, Kind, IsNull, SessionInfo, downcast};
 
 /// An adapter type mapping slices to Postgres arrays.
 ///
@@ -48,14 +48,14 @@ impl<'a, T: 'a + ToSql> ToSql for Slice<'a, T> {
         try!(w.write_i32::<BigEndian>(1)); // has nulls
         try!(w.write_u32::<BigEndian>(member_type.oid()));
 
-        try!(w.write_i32::<BigEndian>(self.0.len() as i32));
+        try!(w.write_i32::<BigEndian>(try!(downcast(self.0.len()))));
         try!(w.write_i32::<BigEndian>(0)); // index offset
 
         let mut inner_buf = vec![];
         for e in self.0 {
             match try!(e.to_sql(&member_type, &mut inner_buf, ctx)) {
                 IsNull::No => {
-                    try!(w.write_i32::<BigEndian>(inner_buf.len() as i32));
+                    try!(w.write_i32::<BigEndian>(try!(downcast(inner_buf.len()))));
                     try!(w.write_all(&inner_buf));
                 }
                 IsNull::Yes => try!(w.write_i32::<BigEndian>(-1)),